1. Field of the Invention
This invention relates to a distance measuring apparatus which implements the steps of (1) emitting a forward laser beam into a detection area, (2) controlling the forward laser beam to scan the detection area, (3) receiving an echo laser beam caused by reflection of the forward laser beam at an object in the detection area, and (4) measuring the time interval between the moment of emission of the forward laser beam and the moment of reception of the corresponding echo laser beam as an indication of the distance to the object. In addition, this invention relates to a radar apparatus.
2. Description of the Related Art
A known distance measuring apparatus mounted on an automotive vehicle intermittently emits a forward laser beam into a detection area in front of the subject vehicle, and controls the forward laser beam to scan the detection area. The known apparatus receives an echo laser beam caused by reflection of the forward laser beam at an object in the detection area. The known apparatus measures the time interval between the moment of emission of the forward laser beam and the moment of reception of the corresponding echo laser beam as an indication of the distance to the object.
A receiver in the known apparatus has a light sensitive area for receiving echo laser beams. The light sensitive area is covered by an array of light sensitive cells. The broadening of the detection area requires an increase in the light sensitive area. A large light sensitive area tends to receive noise laser beams such as a laser beam emitted from a distance measuring apparatus mounted on an oncoming vehicle with respect to the subject vehicle, and an echo laser beam related to a distance measuring apparatus mounted on a vehicle traveling along a lane adjacent to the lane of the subject vehicle. The noise laser beams cause errors in the distance measurement.
U.S. Pat. No. 5,760,886 corresponding to Japanese patent application publication number 7-98381 discloses a scanning-type distance measuring device responsive to selected signals to reduce interference due to stray light or noise light. The device of U.S. Pat. No. 5,760,886 emits a beam of light. The emitted beam of light is reflected from an object and returns to one among photodetectors in a linear array or a two-dimensional array. Selection is made as to the outputs of the photodetectors on the basis of the position of the emitted beam of light. Therefore, photodetectors which should not contribute to the reflected beam are ignored according to the geometry of the emitted beam and the reflecting object. This approach in U.S. Pat. No. 5,760,886 reduces the effects of stray noise from other light sources. The selection of the photodetectors is synchronized with generation of the beam of light by a scanning light emitter in response to a position signal and an angular signal so as to minimize the stray-light-caused noise components of the selection-resultant final output signal.
U.S. Pat. No. 6,301,003 B1 corresponding to Japanese patent application publication number P2000-56018A discloses an optical distance measuring apparatus which transmits a laser beam in a cycle and scans a two-dimensional detection zone by the laser beam. The apparatus of U.S. Pat. No. 6,301,003 B1 includes a light sensitive unit for receiving a return of the laser beam from a target object in the detection zone. Data on the distance to the target object are generated on the basis of the reception of the return of the laser beam. The light sensitive unit is made of a two-dimensional matrix of cells which are selectively activated in each scan cycle for minimizing optical interference with the return of the laser beam from the target object. In each column of the matrix, cells are selectively and sequentially activated. Accordingly, information about the two-dimensional position of the target object is generated.
Japanese patent application publication number 7-280557 discloses a triangulation-based distance measuring apparatus which includes a pair of photosensor arrays. Each photosensor array has a plurality of photodiodes arranged in a line. One or more windows can be provided on each photosensor array. The size of every window is determined by the number of photodiodes composing the window. The number and size of windows on each photosensor array are changed depending on a target distance measurement range. Object images are projected onto the photosensor arrays. Regarding every object, two images are projected onto the photosensor arrays, respectively. The output signals from the photodiodes composing the windows are processed to calculate a phase difference between the object images on the respective photosensor arrays. The distance to an object is computed from the calculated phase difference according to triangulation. The change in the number and size of windows makes it possible to accurately measure both the distance to a near object and the distance to a far object.
Japanese patent application publication number 7-218632 discloses a distance measuring apparatus which includes a laser unit and a photodetector unit. The laser unit has three laser diodes for emitting forward laser beams into three divided regions (transmission-side regions) respectively. The photodetector unit has four photodiodes for receiving echo laser beams from four divided regions (reception-side regions) respectively. The direction along which the reception-side regions are arranged is the same as the direction of the arrangement of the transmission-side regions. The boundaries among the reception-side regions are offset from the boundaries among the transmission-side regions. The laser diodes are sequentially activated in a prescribed order. Thus, a forward laser beam is outputted sequentially from one of the laser diodes. Calculation is carried out about the time interval between the moment of emission of a forward laser beam and the moment of reception of a corresponding echo laser beam. The distance to an object reflecting the forward laser beam and hence causing the echo laser beam is detected on the basis of the calculated time interval. A decision is made as to which of the transmission-side regions corresponds to the forward laser beam. In addition, a decision is made as to which of the reception-side regions corresponds to the echo laser beam. Information about the decided transmission-side region and the decided reception-side region is used in detecting the direction toward the object.
U.S. Pat. No. 5,949,365 corresponding to Japanese patent application publication number 10-288664 discloses a multi-beam radar system in which more transmission elements than reception elements are present. The transmission elements present can be activated both individually and also in any desired simultaneous combination. An observable angular region can thereby be widened. An example of the system in U.S. Pat. No. 5,949,365 includes a first number of transmission elements for transmitting radar waves, and a second number of reception elements for receiving reflected radar waves. The second number is less than the first number. An effective antenna characteristic of the system results from a superimposition of a transmission characteristic of at least one of the transmission elements and a reception characteristic of at least one of the reception elements. The effective antenna characteristic can be modified for at least one measurement cycle by switching between the transmission and reception elements. The transmission elements can be activated individually or simultaneously in a selectable combination.
It is a first object of this invention to provide an improved distance measuring apparatus.
It is a second object of this invention to provide an improved radar apparatus.
A first aspect of this invention provides a distance measuring apparatus comprising scanning and applying means for applying a forward laser beam to a prescribed detection area, and controlling the forward laser beam to scan the detection area along a scanning direction; reflected light detecting means for receiving an echo laser beam caused by reflection of the forward laser beam at an object, the reflected light detecting means including a photodetector array in which a plurality of photo detecting elements are arranged in at least one of the scanning direction and a direction perpendicular to the scanning direction, the photodetector array having a visual field wider than a visual field corresponding to the detection area; changing and selecting means for selecting at least one among the photo detecting elements as an effective element and changing the effective element from one to another in response to a direction of the application of the forward laser beam; time difference measuring means for measuring a time difference between a moment of the application of the forward laser beam by the scanning and applying means and a moment of the reception of the echo laser beam by the reflected light receiving means; distance calculating means for calculating one of (1) a distance to the object and (2) a physical quantity indicative of the distance to the object on the basis of the time difference measured by the time difference measuring means; and correspondence relation grasping means for identifying at least one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a specified direction, and for grasping an actual correspondence relation between directions of the application of the forward laser beam and the photo detecting elements receiving corresponding echo laser beams on the basis of a relation between the identified photo detecting element and the specified direction; wherein the changing and selecting means includes means for selecting at least one among the photo detecting elements as an effective element and changing the effective element from one to another in response to the direction of the application of the forward laser beam according to the actual correspondence relation grasped by the correspondence relation grasping means.
A second aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the correspondence relation grasping means includes (1) means for identifying first one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a first specified direction, (2) means for identifying second one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a second specified direction different from the first specified direction, and (3) means for estimating one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in each of directions different from the first and second specified directions on the basis of a relation between the first and second identified photo detecting elements and the first and second specified directions.
A third aspect of this invention is based on the second aspect thereof, and provides a distance measuring apparatus wherein the first and second specified directions are two among different directions of the application of the forward laser beam, and an angular difference between the two directions is a greatest.
A fourth aspect of this invention is based on the second aspect thereof, and provides a distance measuring apparatus wherein the photodetector array includes a matrix array of photo detecting elements arranged in the scanning direction and also in the direction perpendicular to the scanning direction, wherein the scanning and applying means includes means for controlling the forward laser beam to scan the detection area along the scanning direction and also along the direction perpendicular to the scanning direction, and wherein the first and second specified directions correspond to corners of the detection area respectively.
A fifth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the correspondence relation grasping means includes (1) means for identifying first one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a first specified direction, (2) means for identifying second one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a second specified direction different from the first specified direction, (3) means for identifying third one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a third specified direction different from the first and second specified directions, (4) means for identifying fourth one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in a fourth specified direction different from the first, second, and third specified directions, and (5) means for estimating one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in each of directions different from the first, second, third, and fourth specified directions on the basis of a relation between the first, second, third, and fourth identified photo detecting elements and the first, second, third, and fourth specified directions, wherein the photodetector array includes a matrix array of photo detecting elements arranged in the scanning direction and also in the direction perpendicular to the scanning direction, wherein the scanning and applying means includes means for controlling the forward laser beam to scan the detection area along the scanning direction and also along the direction perpendicular to the scanning direction, and wherein the first, second, third, and fourth specified directions correspond to corners of the detection area respectively.
A sixth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the correspondence relation grasping means includes (1) means for identifying one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in each of all directions of the application of the forward laser beam, and (2) means for grasping the actual correspondence relation on the basis of the identified photo detecting elements.
A seventh aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the correspondence relation grasping means includes (1) means for storing data representing an ideal correspondence relation between directions of the application of the forward laser beam and the photo detecting elements receiving corresponding echo laser beams, (2) means for identifying one among the photo detecting elements which receives an echo laser beam corresponding to the forward laser beam applied in each of at least two different specified directions, (3) means for determining whether or not a relation between the identified photo detecting elements and the specified directions is accorded with the ideal correspondence relation, (4) means for, in cases where it is determined that the relation between the identified photo detecting elements and the specified directions is accorded with the ideal correspondence relation, setting the ideal corresponding relation as the actual correspondence relation, and (5) means for, in cases where it is determined that the relation between the identified photo detecting elements and the specified directions is not accorded with the ideal correspondence relation, grasping the actual correspondence relation on the basis of the relation between the identified photo detecting elements and the specified directions.
An eighth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the correspondence relation grasping means includes means for implementing the identification of the photo detecting element in response to intensities of echo laser beams received by the respective photo detecting elements.
A ninth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the correspondence relation grasping means includes means for implementing the identification of the photo detecting element in response to a center of gravity of a configuration of photo detecting elements receiving respective portions of an echo laser beam.
A tenth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the photodetector array includes a matrix array of photo detecting elements arranged in the scanning direction and also in the direction perpendicular to the scanning direction, and wherein the scanning and applying means includes means for controlling the forward laser beam to scan the detection area along the scanning direction and also along the direction perpendicular to the scanning direction.
An eleventh aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the forward laser beam is of a cross section having a first dimension along the scanning direction and a second dimension along the direction perpendicular to the scanning direction, and the second dimension is greater than the first dimension, and wherein the photodetector array includes a plurality of photo detecting elements arranged in the direction perpendicular to the scanning direction.
A twelfth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus wherein the changing and selecting means includes means for individually selecting one among the photo detecting elements as an effective element and changing the effective element from one to another in response to the direction of the application of the forward laser beam.
A thirteenth aspect of this invention is based on the first aspect thereof, and provides a distance measuring apparatus which is mounted on a vehicle, wherein the scanning direction is equal to one of (1) a direction along a width of the vehicle and (2) a direction along a height of the vehicle.
A fourteenth aspect of this invention provides a radar apparatus comprising a photodetector array including a plurality of photo detecting pixels; first means for emitting a forward laser beam in specified one among prescribed forward beam directions and detecting one among the photo detecting pixels of the photodetector array which receives an echo laser beam caused by reflection of the emitted forward laser beam at an object, the prescribed forward beam directions corresponding to segments of a prescribed detection area respectively; second means for determining a correspondence relation between the prescribed forward beam directions and the photo detecting pixels of the photodetector array on the basis of a relation between the specified forward beam direction and the photo detecting pixel detected by the first means, the determined correspondence relation indicating which of the photo detecting pixels is expected to receive an echo laser beam when the forward laser beam is emitted in each of the prescribed forward beam directions; third means for emitting the forward laser beam and sequentially changing a direction of the emitted forward laser beam among the prescribed forward beam directions to sequentially apply the forward laser beam to the segments of the detection area and thereby scan the detection area; and fourth means for, when the forward laser beam is emitted in each of the prescribed forward beam directions by the third means, selecting one among the photo detecting pixels of the photodetector array as an effective pixel and setting others of the photo detecting pixels as ineffective pixels in accordance with the correspondence relation determined by the second means.
A fifteenth aspect of this invention provides a radar apparatus comprising a photodetector array including a plurality of photo detecting pixels; first means for applying a forward laser beam to specified one among segments of a prescribed detection area and detecting one among the photo detecting pixels of the photodetector array which receives an echo laser beam caused by reflection of the emitted forward laser beam at an object; second means for determining a correspondence relation between the segments of the detection area and the photo detecting pixels of the photodetector array on the basis of a relation between the specified segment and the photo detecting pixel detected by the first means, the determined correspondence relation indicating which of the photo detecting pixels is expected to receive an echo laser beam when the forward laser beam is applied to each of the segments of the detection area; third means for sequentially applying the forward laser beam to the segments of the detection area to scan the detection area; and fourth means for, when the forward laser beam is applied to each of the segments of the detection area by the third means, selecting one among the photo detecting pixels of the photodetector array as an effective pixel and setting others of the photo detecting pixels as ineffective pixels in accordance with the correspondence relation determined by the second means.